Phase 5: AI provider system with local and cloud support

- Implement AIProvider base interface with chat() and is_available()
- Add LocalProvider connecting to bundled llama-server via OpenAI SDK
- Add OpenAIProvider for direct OpenAI API access
- Add AnthropicProvider for Anthropic Claude API
- Add LiteLLMProvider for multi-provider gateway
- Build AIProviderService with provider routing, auto-selection,
  and transcript context injection
- Add ai.chat IPC handler supporting chat, list_providers, set_provider,
  and configure actions
- Add ai_chat, ai_list_providers, ai_configure Tauri commands
- Build interactive AIChatPanel with message history, quick actions
  (Summarize, Action Items), and transcript context awareness
- Tests: 30 Python, 6 Rust, 0 Svelte errors

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

python/voice_to_notes/providers/anthropic_provider.py

@@ -2,4 +2,68 @@
 
 from __future__ import annotations
 
-# TODO: Implement Anthropic provider
+import os
+from typing import Any
+
+from voice_to_notes.providers.base import AIProvider
+
+
+class AnthropicProvider(AIProvider):
+    """Connects to the Anthropic API."""
+
+    def __init__(
+        self,
+        api_key: str | None = None,
+        model: str = "claude-sonnet-4-6",
+    ) -> None:
+        self._api_key = api_key or os.environ.get("ANTHROPIC_API_KEY", "")
+        self._model = model
+        self._client: Any = None
+
+    def _ensure_client(self) -> Any:
+        if self._client is not None:
+            return self._client
+
+        if not self._api_key:
+            raise RuntimeError(
+                "Anthropic API key not configured. Set ANTHROPIC_API_KEY or provide it in settings."
+            )
+
+        try:
+            import anthropic
+
+            self._client = anthropic.Anthropic(api_key=self._api_key)
+        except ImportError:
+            raise RuntimeError("anthropic package is required. Install with: pip install anthropic")
+        return self._client
+
+    def chat(self, messages: list[dict[str, str]], **kwargs: Any) -> str:
+        client = self._ensure_client()
+
+        # Anthropic expects a system message separately
+        system_msg = ""
+        chat_messages = []
+        for msg in messages:
+            if msg.get("role") == "system":
+                system_msg = msg.get("content", "")
+            else:
+                chat_messages.append(msg)
+
+        create_kwargs: dict[str, Any] = {
+            "model": kwargs.get("model", self._model),
+            "messages": chat_messages,
+            "max_tokens": kwargs.get("max_tokens", 2048),
+        }
+        if system_msg:
+            create_kwargs["system"] = system_msg
+
+        response = client.messages.create(**create_kwargs)
+        # Anthropic returns content blocks
+        return "".join(block.text for block in response.content if hasattr(block, "text"))
+
+    def is_available(self) -> bool:
+        return bool(self._api_key)
+
+    @property
+    def name(self) -> str:
+        return "Anthropic"